A large diameter pipeline that is used to convey fluid products such as crude oil or gas over long distances, for example between an oil field and a refinery, between pipelines or between unloading facilities and storage terminals, must occasionally be tested to confirm that there are no leaks in the line which could pose a hazard to the environment, waterways or to individuals or property along the route. Testing also must be performed on all operational pipelines after a leak has been located and repaired, or as required by regulation.
To test a pipeline, a procedure generally known as pressure testing may be used. This involves pressurizing a hydrocarbon liquid in the line to a predetermined value, and monitoring the pressure and temperature of the liquid in the line to determine if there are any leaks. Although a test of an entire pipeline system conceivably could be accomplished in a single operation, it is more typical for a series of independent tests to be made of relatively short-length segments thereof. The pipeline system is typically divided into segments by existing valves. These valves may be anywhere from a few feet to several miles apart. Since testing involves temporary shut-down of the pipeline, which adversely impacts the operation of refineries, terminals and other facilities which depend upon its throughput, there is a compelling need to conduct testing operations as quickly, reliably and economically as possible.
To conduct a meaningful test of a pipeline segment, there must be assurance that the test segment is positively isolated. If the valves that are used to isolate the test segment leak during the test, it is not possible to determine from pressure and temperature data whether the pipeline segment itself will hold pressure or not. Therefore some means should be provided to positively seal off these valves during the test so that if the test pressure drops off, the leak must be somewhere in the segment, not at a valve.
In the past, one process that has been used involved cutting the pipeline and installing test headers to isolate the mainline valves during testing. This procedure is very labor intensive and costly, takes a considerable amount of time, and is destructive to the pipeline. Another technique required blind flanges or a thin metal plate to be inserted between existing flanges. However, this labor intensive method might require draining the line product before installation of the "blinds". Thus the problem of providing a quickly implemented, economical and reliable way to positively seal off a mainline, a branch line or a cross-over valve during a test of a pipeline segment remains unsolved.
An object of the present invention is to provide new and improved methods and apparatus for positively sealing off existing valves in a pipeline which obviates the foregoing problems and difficulties with prior schemes.
Another object of the present invention is to provide new and improved methods and apparatus of the type described where a hydrocarbon gel mixture that can be easily injected into, and removed from, an inner region of a pipeline adjacent an existing valve is used to positively seal off the valve during a pressure test.
Still another object of the present invention is to provide new and improved methods and apparatus of the type described where a hydrocarbon-based highly viscous gel having a lost-circulation material suspended therein is injected into the pipeline adjacent existing valves. The injected gel bridges over and seals off any leakage paths in the valve so that a segment of a pipeline having the valve therein can be tested.